Oxygen saturation is the saturation of the blood with oxygen. A pulse oximeter shows it in a few seconds, without pain and without a blood test. Below are the definitions, normal values, and limits of the method.
What oxygen saturation is
Oxygen saturation is the level of oxygen in the blood.
The mechanism is simple. When you breathe, the lungs take in oxygen and pass it into the blood. Red blood cells carry oxygen-rich blood to the heart, and the heart pumps it to the other organs.
If oxygen saturation drops too low, hypoxemia occurs. It becomes harder for the body to function.
Oxygen saturation is measured by pulse oximetry. This is a non-invasive method of determining the degree of blood oxygen saturation. It is based on a spectrophotometric method.
How oxygen saturation is measured: pulse oximetry
A pulse oximeter is a small device with a clip sensor. The clip is attached to a finger.
Light passes through the skin into the blood. The sensor measures the amount of light. The oxygen level is calculated from this measurement.
After a few seconds, two numbers appear on the screen: pulse rate and oxygen saturation.
The procedure is painless and quick. There are no known risks.
Indications: diseases affecting lung function (COPD, lung cancer, heart failure, asthma, COVID-19), oxygen therapy, anesthesia and the postoperative period, diagnosis of sleep apnea.
Accuracy is limited. The result may be 2–4% higher or lower than the actual blood oxygen level. Arterial blood gas analysis is more accurate.
Which oxygen saturation values are considered normal
The normal range is 95–100%. In healthy subjects it is 97–100%.
Values below this level indicate respiratory failure or limited circulatory impairment.
In lung disease, such as COPD or pneumonia, values may be somewhat lower and considered acceptable.
Values are also lower in high-altitude residents: there is less oxygen in the air there.
What oxygen saturation depends on and why it may decrease
A decrease in oxygen saturation is associated with conditions that affect lung function.
Shortness of breath is a separate symptom. Its common causes: asthma, chest infection, excess weight, smoking, panic attack. More serious ones: COPD, idiopathic pulmonary fibrosis, heart failure, lung cancer. This text does not assert a separate link between these causes and oxygen saturation numbers.
A separate topic is measurement distortion. Pulse oximeter readings are affected by dark nail polish, artificial nails, darker skin pigmentation, poor circulation, cold skin, and smoking.
Why low oxygen saturation is dangerous
The longer the blood oxygen level remains low, the higher the risk of damage to tissues and organs.
Prompt treatment of low oxygen helps avoid serious complications.
Signs of low oxygen level: a bluish tint to the lips, nails, or face; labored breathing and shortness of breath; chest pain or tightness; rapid pulse.
When to see a doctor
Oxygen saturation of 92% or below is a reason to contact a doctor.
Oxygen saturation of 88% or below is a reason to seek medical help immediately.
With shortness of breath, do not try to diagnose yourself. The cause is determined by a doctor.
The doctor evaluates the result together with symptoms and decides whether additional tests are needed, such as arterial blood gases.
A low number on the screen by itself is not a reason to call an ambulance; 103/112 — if the person is gasping for air, cannot say a word, gulps air with the mouth; if the chest is tight or painful and the pain radiates to the arm, back, neck, or jaw; if the lips or skin have become very pale, blue, or gray; if sudden confusion appears.
Terms:
- Oxygen saturation — saturation of the blood with oxygen, in percent.
- Pulse oximetry — non-invasive measurement of oxygen saturation by a spectrophotometric method.
- Pulse oximeter — a device with a finger clip that displays two numbers.
- Hypoxemia — a reduced level of oxygen in the blood.
- Arterial blood gases — a blood test that is more accurate than pulse oximetry.
This material is for reference: it explains the numbers on the screen but does not replace a doctor's consultation.
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This content is for reference and does not replace a doctor's consultation. Medical disclaimer